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At least 217 records · Page 12Linked to original sources
PubMed2006

Variations in the energy metabolism of biotechnologically relevant heterofermentative lactic acid bacteria during growth on sugars and organic acids.

Heterofermentative lactic acid bacteria (LAB) such as Leuconostoc, Oenococcus, and Lactobacillus strains ferment pentoses by the phosphoketolase pathway. The extra NAD(P)H, which is produced during growth on hexoses, is transferred to acetyl-CoA, yielding ethanol. Ethanol fermentation represents the limiting step in hexose fermentation, therefore, part of the extra NAD(P)H is used to produce erythritol and glycerol. Fructose, pyruvate, citrate, and O2 can be used in addition as external electron acceptors for NAD(P)H reoxidation. Use of the external acceptors increases the growth rate of the bacteria. The bacteria are also able to ferment organic acids like malate, pyruvate, and citrate. Malolactic fermentation generates a proton potential by substrate transport. Pyruvate fermentation sustains growth by pyruvate disproportionation involving pyruvate dehydrogenase. Citrate is fermented in the presence of an additional electron donor to acetate and lactate. Thus, heterofermentative LAB are able to use a variety of unusual fermentation reactions in addition to classical heterofermentation. Most of the reactions are significant for food biotechnology/microbiology.

Aldehyde-Lyases↗
PubMed1993

Genetics of bacteriocins produced by lactic acid bacteria.

Lactic acid bacteria produce a variety of bacteriocins that have recently come under detailed investigation. The biochemical and genetic characteristics of these antimicrobial proteins are reviewed and common elements are discussed between the different classes of bacteriocins produced by these Gram-positive bacteria.

Amino Acid Sequence↗
PubMed2006

Structure-function relationships of glucansucrase and fructansucrase enzymes from lactic acid bacteria.

Lactic acid bacteria (LAB) employ sucrase-type enzymes to convert sucrose into homopolysaccharides consisting of either glucosyl units (glucans) or fructosyl units (fructans). The enzymes involved are labeled glucansucrases (GS) and fructansucrases (FS), respectively. The available molecular, biochemical, and structural information on sucrase genes and enzymes from various LAB and their fructan and alpha-glucan products is reviewed. The GS and FS enzymes are both glycoside hydrolase enzymes that act on the same substrate (sucrose) and catalyze (retaining) transglycosylation reactions that result in polysaccharide formation, but they possess completely different protein structures. GS enzymes (family GH70) are large multidomain proteins that occur exclusively in LAB. Their catalytic domain displays clear secondary-structure similarity with alpha-amylase enzymes (family GH13), with a predicted permuted (beta/alpha)(8) barrel structure for which detailed structural and mechanistic information is available. Emphasis now is on identification of residues and regions important for GS enzyme activity and product specificity (synthesis of alpha-glucans differing in glycosidic linkage type, degree and type of branching, glucan molecular mass, and solubility). FS enzymes (family GH68) occur in both gram-negative and gram-positive bacteria and synthesize beta-fructan polymers with either beta-(2-->6) (inulin) or beta-(2-->1) (levan) glycosidic bonds. Recently, the first high-resolution three-dimensional structures have become available for FS (levansucrase) proteins, revealing a rare five-bladed beta-propeller structure with a deep, negatively charged central pocket. Although these structures have provided detailed mechanistic insights, the structural features in FS enzymes dictating the synthesis of either beta-(2-->6) or beta-(2-->1) linkages, degree and type of branching, and fructan molecular mass remain to be identified.

Amino Acid Sequence↗
PubMed2005

Immune responses in mice of beta-galactosidase adsorbed or encapsulated in poly(lactic acid) and poly(lactic-co-glycolic acid) microspheres.

The immune response induced in mice by beta-galactosidase (beta-gal) adsorbed or encapsulated on poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) microspheres was investigated. The encapsulated protein elicited higher antibody response than the protein adsorbed on the microspheres in the case of the PLA microspheres. However, the encapsulated protein elicited weaker antibody response than the adsorbed protein in the case of the PLGA (50:50) microspheres, probably because, in this case, the encapsulation process adversely affected protein immunogenicity. In the case of adsorbed beta-gal, higher antibody response was obtained with the PLA microspheres than with the PLGA (50:50) microspheres. This may be related to the lower rate of beta-gal desorption from the PLA microspheres. Based on the immunoglobulin G1/immunoglobulin G2a ratios and the stimulation indices for interferon-gamma and interleukin-4, beta-gal encapsulated or adsorbed on PLA microspheres induced a Th(1)-biased immune response whereas beta-gal encapsulated or adsorbed on PLGA (50:50) microspheres induced a Th(2)-biased immune response. The results obtained indicate that more potent immune responses are obtained when the protein is encapsulated than adsorbed on the microspheres, providing that the encapsulation process does not adversely affect protein immunogenicity. Also, the type of polymer used to prepare the microspheres, but not the method of protein association with the microspheres, may affect the type of immune response.

Adsorption↗
PubMed2006

Modelling strategies for the industrial exploitation of lactic acid bacteria.

Lactic acid bacteria (LAB) have a long tradition of use in the food industry, and the number and diversity of their applications has increased considerably over the years. Traditionally, process optimization for these applications involved both strain selection and trial and error. More recently, metabolic engineering has emerged as a discipline that focuses on the rational improvement of industrially useful strains. In the post-genomic era, metabolic engineering increasingly benefits from systems biology, an approach that combines mathematical modelling techniques with functional-genomics data to build models for biological interpretation and--ultimately--prediction. In this review, the industrial applications of LAB are mapped onto available global, genome-scale metabolic modelling techniques to evaluate the extent to which functional genomics and systems biology can live up to their industrial promise.

Biomass↗
PubMed1998

Influence of the microencapsulation method and peptide loading on poly(lactic acid) and poly(lactic-co-glycolic acid) degradation during in vitro testing.

Three methods were used, namely spray drying, w/o/w solvent evaporation and the aerosol solvent extraction system (ASES), for the preparation of microparticles having the same size range, to study the influence of the preparation method on polymer degradation in vitro (PBS, 37 degrees C, one month). The following five polymers of the biodegradable poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) group were selected: L-PLA, MW 81 200; DL-PLGA 75:25, MW 64-300; DL-PLGA 50:50 MW 52 600; DL-PLGA 50:50 MW 14 500, AND DL-PLGA 50:50, MW 3400, to prepare drug-free and drug-loaded microparticles. Tetracosactide was selected as model peptide. When microparticles were prepared by solvent evaporation, the mean diameter and, more markedly, the drug encapsulation efficiency tended to decrease when decreasing the molecular weight and increasing the proportion of glycolic acid in the polymer. In contrast, no direct influence of the polymer nature on these parameters was observed in spray dried microparticles. Polymer degradation was heterogenous in L-PLA and DL-PLGA 75:25 microparticles and was not influenced by the presence of the drug at a nominal loading of 1% (w/w), when prepared by the three methods (note that with ASES, only L-PLA could be used for microencapsulation). In batches made of DL-PLGA 50:50 MW 52 600, the degradation rate decreased slightly when increasing the drug loading. Only in the case of DL-PLGA 50:50 MW 14 500, the polymer degradation rate for spray dried microparticles was higher compared to that for microparticles prepared by the w/o/w solvent evaporation method. Generally, the degradation rates of the different microparticles followed the expected order: L-PLA<DL-PLGA 75:50<DL-PLGA 50:50(Mw 52 600)<DLPLGA 50:50 (a mixture of MW 52 600 and MW 3400). Polymer degradation was homogenous in DL-PLGA 50:50 microparticles. Decreasing the molecular weight of DL-PLGA 50:50 from 52 600 to 14 500 did not result in accelerated polymer degradation.

Aerosols↗
PubMed2001

Sequential analysis of malic acid and both enantiomers of lactic acid in wine using a high-performance liquid chromatographic column-switching procedure.

A liquid chromatographic column-switching method for the sequential determination of malic acid and both enantiomers of lactic acid in wine is described. The procedure involves the heart cutting of lactic acid enantiomers from a reversed-phase high-performance liquid chromatography chromatogram, retaining them, and back-flushing them through a chiral ligand-exchange column in which they are separated. The method is used to determine the concentration of lactic acid enantiomers in commercial wines. The results are in satisfactory agreement with those of other methods. The malic acid contents of various wines are also determined. The total analysis time for one experiment is approximately 10 min.

Chromatography, High Pressure Liquid↗
PubMed2007

Individual and combined effects of ph and lactic acid concentration on Listeria innocua inactivation: development of a predictive model and assessment of experimental variability.

In food technology, organic acids (e.g., lactic acid, acetic acid, and citric acid) are popular preservatives. The purpose of this study was to separate the individual effects of the influencing factors pH and undissociated lactic acid on Listeria innocua inactivation. Therefore, the inactivation process was investigated under controlled, initial conditions of pH (pH0) and undissociated lactic acid ([LaH]0). The resulting inactivation curves consisted of a (sometimes negligible) shoulder period followed by a descent phase. In a few cases, a tailing phase was observed. Depending on the conditions, the descent phase contained one or two log-linear parts or had a convex or concave shape. In addition, the inactivation process was characterized by a certain variability, dependent on the severity of the conditions. Furthermore, in the neighborhood of the growth/no growth interface sometimes contradictory observations occurred. Overall, the individual effects of the influencing factors pH and undissociated lactic acid could clearly be distinguished and were also apparent based on fluorescence microscopy. Appropriate model types were developed and enabled prediction of which conditions of pH0 and [LaH]0 are necessary to obtain a predetermined inactivation (number of decimal reductions) within a predetermined time range.

Food Preservatives↗
PubMed1996

Topical 8% glycolic acid and 8% L-lactic acid creams for the treatment of photodamaged skin. A double-blind vehicle-controlled clinical trial.

OBJECTIVE: To evaluate the efficacy and tolerability of 2 widely used topical alpha-hydroxy acids at low concentrations, 8% glycolic acid and 8% lactic (L-isoform) acid creams, in the treatment of photodamaged skin. DESIGN: A single-center, 22-week, double-blind, vehicle-controlled, randomized clinical trial assessed the overall severity of photodamage on the faces and forearms of volunteers, based on 7 individual clinical components of cutaneous photodamage. SETTING: The study was performed in an outpatient clinical research unit at the Massachusetts General Hospital, Boston. PATIENTS: Seventy-four women, aged 40 to 70 years, with moderately severe photodamaged facial skin were enrolled in the study. One subject withdrew from the study early because of skin irritation, and 6 subjects withdrew from the study for personal reasons. INTERVENTIONS: Glycolic acid, L-lactic acid, or vehicle creams were applied twice daily to the face and outer aspect of the forearms. MAIN OUTCOME MEASURES: Improvement in alpha-hydroxy acid-treated photodamaged skin as determined by patient self-assessments and physician evaluations of efficacy and irritancy. RESULTS: The percentage of patients using either 8% glycolic acid or 8% L-lactic acid creams on the face achieving at least 1 grade of improvement (using a scale from 0 through 9) in overall severity of photodamage was significantly greater than with the vehicle cream (76% glycolic acid, 71% lactic acid, and 40% vehicle; P < .05). On the forearms, after 22 weeks, treatment with glycolic acid cream was superior to the vehicle in improving the overall severity of photodamage and sallowness (P < .05). L-Lactic acid cream was significantly superior to the vehicle in reducing the overall severity of photodamage (P < .05), mottled hyperpigmentation (P < .05), sallowness (P < .05), and roughness on the forearms (P < .05) at week 22. CONCLUSIONS: Topical 8% glycolic acid and 8% L-lactic acid creams are modestly useful in ameliorating some of the signs of chronic cutaneous photodamage. These agents are well tolerated and available without prescription.

Administration, Topical↗
PubMed1997

Rapid procedure for acid adaptation of oral lactic-acid bacteria and further characterization of the response.

Acid-adaptive responses could be induced readily in oral lactic-acid bacteria by growing them in batch cultures with excess sugar or more conveniently and rapidly by transferring cells to acidified growth media for the time required for biomass doubling. The response of Streptococcus mutans GS-5 was induced in a progressive rather than all-or-nothing way, and the extent of acid tolerance was inversely related to the pH of the inducing medium over a range from 8.5 to 5. The weak acids fluoride, acetate, or lactate did not measurably enhance acid adaptation, and so the response did not appear to depend primarily on changes in delta pH or the proton motive force across the cell membrane. Transcription and translation to form new proteins did appear to be necessary, as indicated by inhibition of adaptation by rifampin or chloramphenicol and by lack of adaptation by cells suspended in phosphate buffer at pH 5. Streptococcus salivarius and Lactobacillus casei were acid adapted by the rapid method, and the method appeared to be generally useful for oral lactic-acid bacteria. The rapid induction of the response in multiple oral lactic-acid bacteria suggests that it is of general importance for maintaining a diversity of organisms in the oral microbiota, which is regularly subjected to acid stresses.

Acetic Acid↗